Trite nun prepared food (8)
I believe the answer is:
nutrient
'food' is the definition.
(I know that food can be written as nutrient)
'trite nun prepared' is the wordplay.
'prepared' is an anagram indicator.
'trite'+'nun'='tritenun'
'tritenun' is an anagram of 'NUTRIENT'.
(Other definitions for nutrient that I've seen before include "Feeding" , "healthy input" , "Nourishing substance" , "Substance that provides nourishment, may be included in 6 Down" , "Source of nourishment" .)